Generalized plasticity state parameter‐based model for saturated and unsaturated soils. Part 1: Saturated state     

Diego Manzanal  José Antonio Fernández Merodo  Manuel Pastor 《国际地质力学数值与分析法杂志》2011,35(12):1347-1362

The behavior of granular materials is known to depend on its loose or dense nature, which in turns depends both on density and confining pressure. Many models developed in the past require the use of different sets of constitutive parameters for the same material under different confining pressures. The purpose of this paper is to extend a basic generalized plasticity model for sands proposed by Pastor, Zienkiewicz and Chan by modifying the main ingredients of the model flow—rule, loading–unloading discriminating direction and plastic modulus—to include a dependency on the state parameter. The proposed model is tested against the available experimental data on three different sands, using for each of them a single set of material parameters, finding a reasonably good agreement between experiments and predictions. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Generalized plasticity state parameter‐based model for saturated and unsaturated soils. Part II: Unsaturated soil modeling     

Diego Manzanal  Manuel Pastor  José Antonio Fernández Merodo 《国际地质力学数值与分析法杂志》2011,35(18):1899-1917

The aim of this paper is to extend the generalized plasticity state parameter‐based model presented in part 1 to reproduce the hydro‐mechanical behavior of unsaturated soils. The proposed model is based on two pairs of stress–strain variables and a suitable hardening law taking into account the bonding—debonding effect of suction and degree of saturation. A generalized state parameter for unsaturated state is proposed to reproduce soil behavior using a single set of material parameters. Generalized plasticity gives a suitable framework to reproduce not only monotonic stress path but also cyclic behavior. The hydraulic hysteresis during a drying—wetting cycle and the void ratio effect on the hydraulic behavior is introduced. Comparison between model simulations and a series of experimental data available, both cohesive and granular, are given to illustrate the accuracy of the enhanced generalized plasticity equation. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A nonstationary extreme value distribution for analysing the cessation of karst spring discharge          下载免费PDF全文

Yan Liu  Yonghong Hao  Yonghui Fan  Tongke Wang  Xueli Huo  Youcun Liu  Tian‐Chyi J. Yeh 《水文研究》2014,28(20):5251-5258

The effects of climate change and population growth in recent decades are leading us to consider their combined and potentially extreme consequences, particularly regarding hydrological processes, which can be modeled using a generalized extreme value (GEV) distribution. Most of the GEV models were based on a stationary assumption for hydrological processes, in contrast to the nonstationary reality due to climate change and human activities. In this paper, we present the nonstationary generalized extreme value (NSGEV) distribution and use it to investigate the risk of Niangziguan Springs discharge decreasing to zero. Rather than assuming the location, scale, and shape parameters to be constant as one might do for a stationary GEV distribution analysis, the NSGEV approach can reflect the dynamic processes by defining the GEV parameters as functions of time. Because most of the GEV model is designed to evaluate maxima (e.g. flooding, represented by positive numbers), and spring discharge cessation is a ?minima’, we deduced an NSGEV model for minima by applying opposite numbers, i.e. negative instead of positive numbers. The results of the model application to Niangziguan Springs showed that the probability of zero discharge at Niangziguan Springs will be 1/80 in 2025, and 1/10 in 2030. After 2025, the rate of decrease in spring discharge will accelerate, and the probability that Niangziguan Springs will cease flowing will dramatically increase. The NSGEV model is a robust method for analysing karst spring discharge. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Improved algorithms for generalized finite element simulations of three-dimensional hydraulic fracture propagation     

Nathan Shauer  Carlos Armando Duarte 《国际地质力学数值与分析法杂志》2019,43(18):2707-2742

This paper reports improvements to algorithms for the simulation of 3-D hydraulic fracturing with the Generalized Finite Element Method (GFEM). Three optimizations are presented and analyzed. First, an improved initial guess based on solving a 3-D elastic problem with the pressure from the previous step is shown to decrease the number of Newton iterations and increase robustness. Second, an improved methodology to find the time step that leads to fracture propagation is proposed and shown to decrease significantly the number of iterations. Third, reduced computational cost is observed by properly recycling the linear part of the coupled stiffness matrix. Two representative examples are used to analyze these improvements. Additionally, a methodology to include the leak-off term is presented and verified against asymptotic analytical solutions. Conservation of mass is shown to be well satisfied in all examples.  相似文献   

Reaction softening by dissolution–precipitation creep in a retrograde greenschist facies ductile shear zone,New Hampshire,USA          下载免费PDF全文

R. J. McAleer  D. L. Bish  M. J. Kunk  K. R. Sicard  P. M. Valley  G. J. Walsh  B. A. Wathen  R. P. Wintsch 《Journal of Metamorphic Geology》2017,35(1):95-119

We describe strain localization by a mixed process of reaction and microstructural softening in a lower greenschist facies ductile fault zone that transposes and replaces middle to upper amphibolite facies fabrics and mineral assemblages in the host schist of the Littleton Formation near Claremont, New Hampshire. Here, Na‐poor muscovite and chlorite progressively replace first staurolite, then garnet, and finally biotite porphyroblasts as the core of the fault zone is approached. Across the transect, higher grade fabric‐forming Na‐rich muscovite is also progressively replaced by fabric‐forming Na‐poor muscovite. The mineralogy of the new phyllonitic fault‐rock produced is dominated by Na‐poor muscovite and chlorite together with late albite porphyroblasts. The replacement of the amphibolite facies porphyroblasts by muscovite and chlorite is pseudomorphic in some samples and shows that the chemical metastability of the porphyroblasts is sufficient to drive replacement. In contrast, element mapping shows that fabric‐forming Na‐rich muscovite is selectively replaced at high‐strain microstructural sites, indicating that strain energy played an important role in activating the dissolution of the compositionally metastable muscovite. The replacement of strong, high‐grade porphyroblasts by weaker Na‐poor muscovite and chlorite constitutes reaction softening. The crystallization of parallel and contiguous mica in the retrograde foliation at the expense of the earlier and locally crenulated Na‐rich muscovite‐defined foliation destroys not only the metastable high‐grade mineralogy, but also its stronger geometry. This process constitutes both reaction and microstructural softening. The deformation mechanism here was thus one of dissolution–precipitation creep, activated at considerably lower stresses than might be predicted in quartzofeldspathic rocks at the same lower greenschist facies conditions.  相似文献   

南沙群岛海域长腹剑水蚤(Oithona spp.)的种类组成、数量分布及其与环境因子的关系   总被引：1，自引：0，他引：1  

杜飞雁  王亮根  王雪辉  宁加佳  谷阳光  李亚芳 《海洋与湖沼》2016,47(6):1176-1184

中小型桡足类是海洋食物网中重要的中间环节,在碳循环里细菌碳和藻类碳向高营养级转化的过程中扮演重要角色。本文通过分析2013年3—4月、6—7月、9—10月和11—12月南沙群岛海域(111°30′E—112°30′E,4°30′N—11°30′N)的生态环境调查数据,对长腹剑水蚤属(Oithona)的种类组成、数量分布及其与环境因子的关系进行了研究。结果表明:(1)南沙群岛海域共出现长腹剑水蚤15种(包括1个未定种),其中线长腹水蚤(Oithona linearis)、粗长腹剑水蚤(O.robusta)和长刺长腹剑水蚤(O.longispina)为南沙群岛海域首次记录,长腹剑水蚤属种类组成沿水深变化的现象较为明显,该属虽然在南沙群岛海域广泛分布,但单种的出现频率较低,其种类出现的季节性较强;(2)南沙群岛海域的长腹剑水蚤可以划分为常见广布组群Ⅰ和低频组群Ⅱ;(3)长腹剑水蚤年均栖息密度为30ind./m3,季节变化呈单峰型,秋季最高、冬季最低,高数量区主要出现在受南沙西部沿岸流和东部沿岸流影响的近岸海域;(4)在0—750m水深范围内,长腹剑水蚤数量沿水深梯度的垂直变化明显,呈现由浅至深数量明显减少的趋势,长腹剑水蚤主要集中分布在0—75m的水层中,75—500m数量急剧降低至最低后,在500—750m基本维持不变;(5)GAM分析表明,纬度、海水温度、盐度和叶绿素a浓度对长腹剑水蚤数量均有影响,以纬度的影响最为显著,其中长腹剑水蚤属最适温度为28.6—29.2℃,最适盐度为32.6—33.2,最适叶绿素a浓度为5—10μg/L;(6)长腹剑水蚤属更适栖息于低温和低盐,且受沿岸流影响的环境中。因此,其数量分布的季节变化与季风驱动的沿岸流势力强弱密切相关。  相似文献   

雅鲁藏布江流域极端降水模拟及预估     

高佳佳  杜军 《冰川冻土》2021,43(2):580-588

为了解雅鲁藏布江流域汛期极端降水的变化规律,推算一定重现期的极端降水量分位数,通过百分位法、Hill图法、年交叉率法选取阈值,借助广义帕累托分布函数（GPD）对流域极端降水频率进行了分析。结果表明：99百分位时的阈值为流域内各站点的最佳阈值,且各站点超阈值序列通过了M-K的平稳性检验,无明显突变。拟合效果通过K-S检验,各站点拟合的极端降水理论频数和实测频数基本相符。尺度参数的大值区位于流域下游,表明该地区的极值波动大;形状参数正值区位于流域中上游地区,说明发生破纪录降水事件的概率较大,拟合结果与实际观测一致。从5年一遇和10年一遇的极端降水值来看,雅江流域除拉孜站外,其他地区降水极值均超过30 mm,日喀则地区的降水极值达50 mm;各地区20年一遇和30年一遇的降水极值增长的非常缓慢。通过与实际极端降水值对比分析得出,GPD拟合计算出的重现期水平基本符合实际,即具有一定的合理性。  相似文献   

华北北部不同构造单元地壳速度模型——均匀分层介质反射波走时反演的结果   总被引：1，自引：0，他引：1  

田晓峰  张先康  嘉世旭  杨卓欣  段永红  徐朝繁  张成科  张健狮 《华北地震科学》2006,24(3):1-5

从广义反演理论出发,对多层反射波的走时联合反演,可以同时获得所有的各层速度及厚度参数。其优点是在不需要把问题线性化过程的同时,统一考虑了各层反射波走时的离散对整个地壳模型的影响,又可兼顾观测数据的不同误差分布。本文将该方法进行了数值模拟并应用于华北北部的几个不同构造单元,反演得出了其反射P波速度结构,并与正演结果进行了对比。  相似文献   

山东南部近海秋季长蛇鲻相对资源量的分布及其影响因素     

刘逸文  张崇良  昝肖肖  孙铭  徐宾铎  薛莹  任一平 《中国海洋大学学报(自然科学版)》2020,50(4):45-53

为探究长蛇鲻(Saurida elongate)的生态习性和分布规律,并为长蛇鲻资源的合理利用与养护提供科学依据,本文根据2016年秋季在山东南部近海进行的渔业资源与环境调查数据,分析了该海域长蛇鲻的分布特征,研究长蛇鲻成体、幼体的分布差异,并利用广义可加模型(GAM)研究其分布与生物因子和环境因子的关系。结果表明,长蛇鲻成体与幼体的分布存在差异,成体分布范围广,幼体主要分布在30 m等深线及以浅水域。GAM模型的结果表明,饵料生物、底层水温、水深和底层盐度是影响长蛇鲻相对资源量分布的主要因子。成体、幼体的分布与影响因子的关系差异极显著(P<0.01)。长蛇鲻成体的相对资源量随饵料生物和底层水温的增加表现为先上升后下降的趋势,而幼体呈现一致上升趋势;成体和幼体的相对资源量随水深增加均呈下降趋势;幼体相对资源量随底层盐度增加有明显上升趋势,而盐度对成体的影响不显著。本研究认为山东南部近海是长蛇鲻的重要栖息地,水温和盐度是成体和幼体分布差异的可能原因。  相似文献   

应用分块矩阵求逆解算约束秩亏间接平差模型     

谢波  刘连旺 《大地测量与地球动力学》2021,41(2):157-161

在通常的四分块矩阵求广义逆矩阵和凯利逆矩阵公式基础上,分析左上角子矩阵为秩亏、右下角子矩阵为零的特殊四分块矩阵的凯利逆矩阵存在条件,应用广义逆矩阵法和矩阵变换法推导该类特殊四分块矩阵的凯利逆矩阵显性表达公式,并用于解算约束秩亏间接平差模型的参数估计.实验数据表明,当满足存在性条件时,应用分块矩阵求逆公式解算约束秩亏间接...  相似文献